U.S. Pat. No. 4,444,817 and U.S. Pat. No. 4,410,482 (Subramanian) disclose shaped articles comprising a polyolefin matrix and a dispersed polyamide phase in the form of thin sheets or plates, the latter however being produced partly by mixing of the polyolefin and polyamide, and partly by the transformation into web or hollow body form, as these operations lead to the polyamide being stretched into thin sheet or plate form. The product comprises a polyethylene matrix containing thin copolyamide 6/6,6 plates or sheets (in other words the polymer produced by condensation of hexamethylene diamine, adipic acid and caprolactame). It is also necessary to add a compatibilizer, this being grafted (using fumaric acid) polyethylene causing the thin plates or sheets to adhere to each other and/or to the matrix, as otherwise the objects have no mechanical propertied or cannot even be manufactured. This compatibilizer is present between the thin plates or sheets and the matrix, and bonds them together (U.S. Pat. No. 4,410,482) or is present between the thin plates or sheets and is responsible for the latter adhering together (U.S. Pat. No. 4,444,817).
According to these references, the 6/6,6 copolyamide is prepared in the form of cubic pellets of 3 to 4 mm on a side. The cubic 3 to 4 mm on a side pellets, polyamide and compatibilzer in the form of 2 to 3 mm on a side pellets are mixed in the dry state until a homogeneous mixture is obtained. Following this, the mixture is heated to above the highest melting temperature of the three components, taking care not to provide an intimate mixture as, otherwise, the copolyamide comes out in the form of spherical nodules rather than thin sheets or plates. The principle consists in subjecting this heterogeneous mixture to shear and/or stretching forces. The effects of extruding and blowing the parison are combined. Following this, it is cooled down to below the lowest melting temperature of the components. The copolyamide can be replaced by polyester or polycarbonate. This technique requires very strict control of the operating conditions, of the polymers and of their melt index to ensure it is reproducible. If stretching is insufficient, thin sheets or plates are not obtained, and if the mixture is too homogeneous, nodules and not thin plates or sheet result. Only the structure with thin plates or sheets provides barrier properties towards unleaded gasoline, compared with other structures.
WO 95/11939 discloses the same principle, but the thin plates are inside a mixture of 6/6,6 copolyamide and phenolic resin. As above, this structure is difficult to reproduce.
EP-A-0,622,183 discloses multi-layer films one of the layers of which consists of a recycled product of polyamide and polyolefin and a binder, the recycled product constituting 60 to 98% by weight of the layer. The recycled product can be a "regenerated product" (granulated after melting with additives), a "regranulated product" (granulated after melting without additives) or an "agglomerate" (without melting). The binder can be a functionalized polyolefin, for example a polyolefin functionalized with maleic anhydride. This document does not mention barrier properties or improved mechanical properties, nor does it describe the physical characteristics of the mixture; additionally, the manufacturing process requires several layers to be present in order to obtain a product suitable for use.
Thus, these references disclose mixtures comprising a polyolefin and a polyamide which are, on the one hand, in the form of a polyolefin matrix containing polyamide plates or sheets and, on the other hand, in the form of multilayer films.
However, the references mentioned above do not provide a mixture which always has good barrier properties combined with good mechanical properties; additionally, the references do not provide a process which can easily be carried out.
The invention provides a solution to these problems and additionally provides supplementary advantages.